The call comes after destructive North American signal crayfish were discovered in waters at Lochrutton for the first time last year.
The invasive shellfish have already caused severe ecological damage to Loch Ken at New Galloway.
Now fears are mounting that it will only be a matter of time before they do the same to the River Nith.
As the salmon season opened on Monday, fishing groups urged anglers to watch out for crayfish and to report any sightings.
The Nith Fishery Trust has been surveying the lower river for the shellfish since sightings were reported near Kingholm Quay, Dumfries.
Dumfries & Galloway Standard